Optical reflector assemblies for use optical rotary joints

ABSTRACT

The present invention relates generally to optical rotary joints ( 35 ) for enabling optical communication between a rotor and a stator, and to improved optical reflector assemblies for use in such optical rotary joints.

TECHNICAL FIELD

The present invention relates generally to optical rotary joints forenabling optical communication between a rotor and a stator, to improvedmethods of mounting such optical rotary joints on supporting structuressuch that the rotor and stator remain properly aligned, and to improvedoptical reflector assemblies for use in such optical rotary joints.

BACKGROUND OF THE INVENTION

This invention provides improvements to various communication devicesdescribed in U.S. Pat. No. 6,980,714, dated Dec. 27, 2005, to K. PeterLo and Norris E. Lewis, entitled “Fiber Optic Rotary Joint andAssociated Reflector Assembly”. The communication devices described inthe '714 patent are capable of transmitting data and/or power(hereinafter sometimes jointly and severally referred to as“communication”) across a rotary interface, such as between a rotor anda stator.

For example, computed tomography (CT) scanners require data transmissionacross a rotary interface. In order to enable such data transmission,slip rings are commonly employed. A slip ring has a rotating elementthat rotates with the rotor, and a stationary element affixed to thestator. Slip rings were originally designed to support electricalcommunication between the rotor and stator. However, as data ratesincreased, electrical transmission of the data became impractical.Optical rotary joints were then developed to support higher datatransmission rates across the rotary interface. Optical communication iscapable of transmitting data at much higher rates than prior electricalcommunication techniques.

Previous techniques in optical communication across a rotary interfacehave included the use of waveguides (see, e.g., U.S. Pat. No. 6,453,088,dated Sep. 17, 2002, to Norris E. Lewis, Anthony L. Bowman and Robert T.Rogers, entitled “Segmented Waveguide for Large Diameter Fiber OpticRotary Joint”; U.S. Pat. No. 6,104,849, dated Aug. 15, 2000, to NorrisE. Lewis, Anthony L. Bowman, Robert T. Rogers and Michael P. Duncan,entitled “Fiber Optic Rotary Joint”; and U.S. Pat. No. 5,991,478, datedNov. 23, 1999, to Norris E. Lewis, Anthony L. Bowman, Robert T. Rogersand Michael P. Duncan, entitled “Fiber Optic Rotary Joint”), opticalfibers (see, e.g., U.S. Pat. No. 6,650,843, dated Nov. 18, 2003, toGeorg Lohr, Markus Stark and Hans Poisel, entitled “Device for theOptical Transmission of Signals”), and free space propagation (see,e.g., Japanese Pat. Pub. No. 09-308625, dated Feb. 12, 1997, to SuzukiTatsuro, Teimoshii Aari Fuotsukusu and Tomu Haatofuoodo, entitled“Optical Transmission System”). The aggregate disclosures of thesereferences are hereby incorporated by reference with respect to thestructure and operation of such prior art optical rotary joints.

In CT scanner applications, in which the axis of rotor rotation issometimes physically occupied by a patient, off-axis rotary joints aregenerally employed to transmit signals between the rotor and stator.Such off-axis rotary joints generally include one or more light sourcesfor emitting the optical signals, and arcuate reflectors havingchannel-shaped transverse cross-sections that receive such transmittedsignals and direct such received signals to respective light receivers.The optical sources are spaced circumferentially about one of the rotorand stator, while the reflectors and receivers are spacedcircumferentially about the other of the rotor and stator. The opticalsources may include one or more common light sources, the opticalsignals from which are directed, as by optical fibers, to the peripheryof the associated one of the rotor and stator, or may be separateemitting elements mounted about such periphery. For example, the opticalsources may be disposed circumferentially about the rotor, while themultiple reflectors and receivers may be disposed circumferentiallyabout the stator, thereby supporting optical communications from therotor to the stator. In most cases, the path of optical datatransmission across the rotary joint (i.e., between the rotor andstator) is in a radial direction with respect to the rotor axis. Inother words, if light is transmitted from the rotor to the stator, thelight is seen as coming from the rotor axis, for example, regardless ofthe physical location of the light source(s).

In operation, each of the light sources may possibly transmit the sameoptical signal. These signals may be transmitted across the rotaryinterface, and may be received by one or more of the reflectors and bedirected to the associated receivers, depending upon the angularposition of the rotor relative to the stator. In other embodiments,different optical signals may be transmitted from different lightsources, or may be multiplexed if coming from the same source.

While generally effective for permitting optical communication between arotor and a stator, conventional off-axis rotary joints that employ sucharcuate reflectors with channel-shaped cross-sections suffer fromseveral shortcomings, especially at higher data transmission rates.These problems include: (a) the broadening of superimposed pulse widthsdue to different-length light transmission paths, and (b) that a greaternumber of light sources must be used when transmitting signals into theentrance end of an optical fiber than when such signals are incidentdirectly upon a photodetector, as discussed infra.

For example, in conventional off-axis rotary joints, the optical signalsmay travel along different-length paths between the various sources andthe respective receivers, thereby introducing time delays in the variousreceived optical signals, when superimposed. A particular receiver mightreceive signals from two circumferentially-adjacent optical sources. Ifthe same optical signal is simultaneously emitted by the two adjacentsources, but such signals travel different distances to reach thereceiver, the signals will be received at different times. Accordingly,the two signals will be out-of-phase, and the pulse width of thesuperimposed signals, as seen by the receiver, will be effectivelybroadened. To support communication at the desired high data rates,conventional off-axis rotary joints have been specifically designed tohave less spacing between the optical sources and the receivers so as tominimize the path lengths of signal travel. Even so, it is difficult tosupport error-free data transmission at a data rate above 1.25 Gbit/sec,where the signals travel along different-length paths.

The aforesaid '714 patent discloses an optical rotary joint and anassociated reflector assembly to provide optical communication between arotor and a stator. By designing the optical rotary joint such that theoptical signals travel along paths of equal path, the pulse width of thesuperimposed optical signals, as seen by the receiver, will not beincreased.

To effect this, the '714 patent contemplates that the rotary jointinclude a reflector assembly having a concave elliptical reflectingsurface, and possibly a hyperbolic reflecting surface as well. Bothshapes are conic-section curves in a Cartesian plane (i.e., defined bythe x-y axes) defined by the general equation:Ax ² +Bxy+Cy ² +Dx+Ey+F=0where A, B, C, D, E and F are constants. For an ellipse, B²<4AC; for ahyperbola, B²>4AC. For an ellipse, the sum of the distances from anypoint on the curve to the two focal points (F₁, F₂) is a constant. Ifthe reflecting surface is configured as a portion of an ellipse, lightissuing from one focal point will be reflected by such ellipticalreflecting surface toward the other focal point. However, the totallength of the path of light traveling from one focal point to the otherwill be a constant, regardless of the specific location of the point onthe elliptical reflecting surface on which the emitted light isincident. Conversely, for a hyperbolic reflecting surface, thedifference between the distances from any point on the curved reflectivesurface to the two fixed focal points is a constant.

The '714 patent discloses several different optical configurations. Insome of these, the received signals are focused directly on aphotodiode. In other configurations, the reflected signals are focusedon the entrance end of an optical fiber that communicates with aphotodiode at a remote location. In still other configurations, afocusing lens is positioned at the entrance end to direct the receivedsignals into the optical fiber.

However, the acceptance angle of an optical fiber is more limited thanthat for a photodiode. The main reason for this is that an optical fiberhas a more limited numerical aperture (NA), than does a photodiode. Themore-limited NA of an optical fiber restricts the approach angle atwhich light can be directed and guided into the fiber. This, in turn,limits the design of the reflective surfaces by means of which light maybe directed toward the entrance end of the receiving fiber. Thislimitation requires, as a practical matter, that a greater number oflight sources be used when the transmitted signals are to be directedinitially into an optical fiber, than when such signals are incidentdirectly on a photodetector.

Referring now to the drawings, FIGS. 1 and 2 of the present applicationcorrespond substantively to FIGS. 1 and 2 of the '714 patent, except forthe differences in the reference numerals. Thus, these figures disclosea prior art optical rotary joint, generally indicated at 20, in whichthe various light sources 21 are mounted on the rotor 22. The opticalbeams are directed radially outwardly, as if they were coming from focalpoint F₁ at the rotor's axis of rotation. The beams are incident on theelliptical reflecting surface 23 of reflector 24, and are reflectedbackwardly toward the conjugate focal point F₂. However, such reflectedbeams are incident on, and are re-reflected forwardly by, hyperbolicreflecting surface 25 positioned between the elliptical reflectingsurface and the back focal point B, and such forwardly-reflected beamsare focused on receiver 26 which is located at the conjugate focal pointC. The back focal point B of hyperbolic reflecting surface 25 iscoincident with conjugate focal point F₂ of elliptical reflectingsurface 23.

The '714 patent discloses an optical rotary joint that allows thetransmission of high bandwidth optical signals from the rotor to thestator, and vice versa. In the scenario in which optical signals aretransmitted from the rotor to the stator, a number of light sources arespaced evenly around the periphery of the rotor. The number of lightsources required for continuous transmission of data across the rotaryinterface depends on the acceptance angle, θ, of the ellipticalreflector. The acceptance angle θ is defined as the angle of theelliptical reflective surface, measured from the center of the rotorwithin which the light rays from the source can be directed and guidedinto the receiver. The acceptance angle θ is a function of the opticalpath length and the acceptance angle φ of the receiving fiber orphotodetector (as appropriate), where:φ=2×sin⁻¹(NA)

To insure that optical communications can be continuously transmitted,at least one optical source has to be within the acceptance angle of theelliptical reflector at all relative angular positions of the rotor andstator. For example, if the receiving fiber has an NA of 0.37, theacceptance angle φ of this configuration is 13.6°, as shown in FIG. 3.Beyond the limits of this acceptance angle, the optical signals simplyattenuate in the cladding layer of the fiber, and do not reach thephotodetector. To populate the rotor circumference with evenly-spacedlight sources such that at least one source is within the acceptanceangle of the receiving fiber at all such relative angular positions, atleast twenty-seven sources are required (i.e., 360°/13.6°=26.47≈27sources).

On the other hand, if a photodetector is used as the receiver, and ifthe photodetector has an NA of 0.74 such that its acceptance angle φ iswidened to 32°, then only twelve circumferentially-spaced light sourcesare needed to populate the rotor so as to assure continuouscommunication (i.e., 360°/32°=11.25≈12 sources). Depending on theparticular design of the photodiode package, the acceptance angle can beas high as 140° (NA=0.94).

Thus, to reduce the number of sources and to reduce cost and systemcomplexity, it would be more advantageous to have the received signalsare incident directly on a photodetector, rather than be first directedinto the entrance end of an optical fiber for transmission therealong toa remotely-located photodetector. Moreover, a shorter path length to thephotodetector is also desirable to reduce angular tolerance issues in aproduction environment.

Referring now to FIG. 4 of the present application, which substantivelycorresponds to FIG. 4 of the '714 patent except for the differences inthe reference numerals, the '714 patent also discloses an embodiment,generally indicated at 28, in which a single elliptical reflector 29 isused (i.e., without a cooperative hyperbolic reflector), and theconjugate focal point F₂ lies radially outside of the rotor. In thisarrangement, reflector 29 has an elliptical reflective surface 30operatively arranged to focus the beams emanating radially outwardlyfrom sources 31 into the entrance end of an optical fiber 32 thatcommunicates with a remotely-located photodetector (not shown). Theentrance end of the optical fiber is coincident with the conjugate focalpoint F₂ of the elliptical reflector.

If the reflected light is directed into optical fiber 32, the limited NAof the receiving fiber again requires that a large number of lightsources to be spaced equally about the circumference of the rotor. Forexample, when the NA of the fiber is 0.37, using geometrical analysis,the acceptance angle of the reflector, θ, is 9.7°, with an optical pathlength of 210 mm from the edge of the rotor to the receiver. To populatethe rotor such that continuous transmission of data from the rotor tothe stator is assured, at least thirty-eight light sources are required(i.e., 360°/9.7°=37.11≈38 sources).

These two examples demonstrate that when the reflected light beams areincident directly on a receiver having a larger NA, such as aphotodetector as opposed to the entrance end of an optical fiber leadingto the receiver, the number of light sources, and hence the cost andcomplexity of the system, may be reduced.

While the fiber optic rotary joint in the '714 patent can enable highdata transmission across a rotary interface, it would be desirable toprovide improved versions of such constant-path-length fiber opticrotary joints that are capable of transmitting optical signals at ratesgreater than about 1.25 Gbit/s, that have lower insertion losses, thatare more compatible with the use of optical fibers leading to remotereceivers, that use smaller numbers of light sources, and that haveminimum optical path lengths

DISCLOSURE OF THE INVENTION

With parenthetical reference to the corresponding parts, portions orsurfaces of the disclosed embodiment, merely for purposes ofillustration and not by way of limitation, the present invention broadlyprovides improved optical rotary joints, improved methods of mountingsuch optical rotary joints on supporting structure, and improved opticalreflector assemblies for use in such optical rotary joints.

In a first aspect, the invention provides an improved optical rotaryjoint (35) for enabling optical communication between a rotor and astator, the rotor having a longitudinal axis, comprising: at least oneoptical source (36) mounted on one of the rotor and stator fortransmitting an optical signal in a radial direction with respect to thelongitudinal axis of the rotor; at least one first reflector (38)mounted on the other of the rotor and stator for reflecting the opticalsignal transmitted from the source, the first reflector comprising aconcave first reflective surface (44), a line (L) in a plane takenthrough the first reflective surface being configured as a portion of anellipse having first and second focal points (F₁, F₂), the first focalpoint being positioned substantially coincident with the rotor axis; asecond reflector (39) having a second reflective surface (45) configuredas a portion of a cone and positioned at the second focal point of theelliptical surface for receiving light reflected from the firstreflective surface and for reflecting light in a different direction asa function of the apex angle of the second reflective surface; and areceiver (40) arranged to receive light reflected by the secondreflective surface.

In the preferred form, the first reflective surface (44) is configuredand arranged such that the area of light that is incident on the secondreflective surface is smaller than the area of light that is incident onthe first reflective surface. Preferably, the light reflected from thefirst reflective surface is focused on a spot on the second focal point,F₂. The first reflective surface may be configured as a portion of anellipsoid. As used herein, an ellipsoid is defined as being a geometricsurface, all of whose plane sections are either ellipses or circles.

A first plurality of the optical sources may be mounted on the one ofthe rotor and stator, and a second plurality of the first reflectors aremounted on the other of the rotor and stator. The first and secondpluralities may not be the same.

The improved optical rotary joint may further include: an optical fiber(41) having an entrance end and an exit end. The entrance end may bearranged at, or proximate to, the second focal point. The receiver maybe arranged at, or proximate to, the exit end. The receiver may be aphotodiode.

The improved rotary joint may further include: a lens assembly (40)arranged proximate the second focal point adjacent to the entrance endfor guiding light into the optical fiber (41). This lens assembly mayinclude a series of lenses, such as two plano-convex lenses, a lens anda holographic element, etc.

The improved rotary joint may further include: a prism for furtherchanging the direction of the light rays reflected by the secondreflective surface.

Preferably, a light ray traveling from the source to the receiver has asubstantially constant path length regardless of the relative angularposition between the rotor and stator. Moreover, the operation of theoptical rotary joint is desirably independent of both the wavelength ofthe optical signal and the data rate of the signal.

Intensity variations of light falling incident on the receiver, arereduced to meet the dynamic range limitations of the receiver. Thesecond reflective surface may have an apex angle of about 45°.

In the preferred embodiment, the optical signals are transmitted in aplurality of data channels. The maximum transmission data rate of theoptical rotary joint is the sum of the number of channels times themaximum data rate per channel. Each channel may be capable oftransmitting data at rates of 5.0 Gbit/sec or more. In one particularform having sixteen channels, the maximum data rate is on the order ofabout 80 Gbit/sec.

The second reflective surface may be conical.

The improved joint may further include a crosspoint switch having Ninputs and M outputs and/or multiple light sources having differentwavelengths, with the optical signals being wavelength divisionmultiplexed.

In another aspect, the invention provides: an optical rotary joint (35)for enabling optical communication between a rotor and a stator, therotor having a longitudinal axis, comprising: at least one opticalsource (36) mounted on one of the rotor and stator for transmitting anoptical signal in a radial direction with respect to the longitudinalaxis of the rotor; at least one first reflector (38) mounted on theother of the rotor and stator for reflecting the optical signaltransmitted from the source, the first reflector comprising a firstreflective surface (44), a line (L) in a plane taken through the firstreflective surface being configured as a portion of an ellipse havingfirst and second focal points (F₁, F₂), the first focal point beingpositioned substantially coincident with the rotor axis; a receiver (48,49) arranged to receive light; and at least one light guide (47) havingan entrance end positioned proximate the second focal point and havingan exit end, and wherein the light guide includes a fiber arrayincluding a bundle of optical fibers having closely-adjacent entranceends positioned proximate the second focal point and having exit ends,and wherein the fiber array is operatively arranged to guide lighttoward the receiver.

In this form, the entrance ends may have a convex shape. The secondfocal point may be arranged interiorly of, exteriorly of, or on, theconvex shape. The entrance ends may be configured as a segment of acylinder. The entrance ends of the fibers may be configured as a slab,and may possibly have a convex surface. A tapered slab waveguide may beused to guide light to the receiver.

The receiver may be a photodiode (49) having an active area, and lightmay be directed from the exit ends of the fibers toward the active area.A lens (48) may be positioned between the exit ends and the photodiodefor directing light toward the photodiode.

In the preferred form, the path of light propagation from the entranceends to the receiver is substantially the same for each of the fibers,and the lengths of the fibers are substantially the same.

In another aspect, the invention provides an optical reflector assembly(50) for enabling optical communication between a rotor and a stator,the rotor having a longitudinal axis, comprising: a first member (51)having a concave first reflective surface (52), a line (L) in a planetaken through the first reflective surface being configured as a portionof an ellipse having first and second focal points (F₁, F₂), the firstfocal point being positioned substantially coincident with the rotoraxis; a second member (53) mounted on one side of the first member; athird member (56) mounted on the opposite side of the first member; afourth member (54) mounted on the second member and having a secondreflective surface (55) configured as a portion of a cone, the secondreflective surface having a longitudinal axis, the second focal pointbeing positioned substantially on the second reflective surface; and areceiver (58) mounted on the third member such that light seen asoriginating from the first focal point and being incident on the firstreflective surface will be reflected toward the second reflectivesurface, and such reflected light being incident on the secondreflective surface will be further reflected toward the receiver.

The receiver may be substantially aligned with the second reflectivesurface longitudinal axis.

The first reflective surface is configured and arranged such that thearea of second reflective surface upon which light from the firstreflective surface is incident is preferably smaller than the area offirst reflective surface upon which light from the source is incident.To achieve this, the first reflective surface may be configured as aportion of an ellipsoid.

In one particular form, the first member is a plate-like member havingopposite planar surfaces, the second member has a planar surfacearranged to engage one of the first member planar surfaces, and thethird member has a planar surface arranged to engage the other of thefirst member planar surfaces. The second and third members may beplate-like members. The second reflective surface may be conical, andmay have an apex angle of about 45°.

The receiver may be substantially aligned with the second reflectivesurface longitudinal axis. The receiver may include receiving opticsmounted on the third member and substantially aligned with the secondreflective surface longitudinal axis, and a optical fiber having andentrance end arranged to receive light from the receiving optics andhaving an exit end, and a photodiode arranged at the receiving end. Thereceiving optics may include an aspheric lens and a ball lens, a pair ofaspheric lenses, or the like.

In still another aspect, the invention provides a method of mounting anoptical rotary joint on a supporting frame, comprising the steps of: (a)providing a tooling plate (60) having an annular inner portion (61)provided with a plurality of circularly-spaced radially-extendingV-grooves (62), and having an arcuate outer portion (63) provided with aplurality of circularly-spaced pockets (64), each pocket being adaptedto receive and hold a reflector assembly in a predetermined positionrelative to the proximate V-grooves; (b) providing a plurality ofoptical reflector assemblies (50); (c) placing an optical reflectorassembly in each pocket; (d) providing a plurality of assembled opticalcollimators in said tooling plate V-grooves and testing the integrity ofthe optical connection between said fiber and collimator assembly andthe proximate optical reflector assembly; (e) providing a statorsegment; (f) placing said stator segment on said optical reflectorassemblies; (g) mounting the optical reflector assemblies to the statorsegment to form an assembled stator; (h) removing the said assembledstator from the tooling plate; (i) placing cylindrical gauge pins (65)in at least some of the V-grooves; (j) providing a plurality of rotorsegments (66), each rotor segment having a plurality ofcircularly-spaced radially-extending V-grooves; (k) placing the rotorsegments such that the gauge pins are received in the rotor segmentV-grooves; (l) joining the rotor segments to form an assembled rotor(68); (m) removing the assembled rotor from the tooling plate; (n)inverting said assembled rotor; (o) providing a plurality of fiber andcollimator assemblies; (p) mounting said fiber and collimator assembliesin said assembled rotor V-grooves; (q) providing a plurality ofbrackets; (r) mounting the brackets on the assembled rotor and thestator segment to maintain the alignment of the collimator assemblieswith the optical reflector assemblies; (s) mounting the assembled rotorand stator segment on the supporting frame; and (t) removing thebrackets; thereby to mount the assembled rotor and stator on thesupporting frame in the desired optical alignment with respect to oneanother.

Accordingly, the general object of the invention is to provide animproved optical rotary joint.

Another object is to provide an improved method of mounting an opticalrotary joint on supporting structure so as to maintain a desiredalignment between the rotor and stator.

Still another object is to provide an improved optical reflectorassembly for use in an optical rotary joint.

These and other objects and advantages will be come apparent from theforegoing and ongoing written specification, the drawings, and theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of an prior art optical rotaryjoint including a reflector assembly having an elliptical reflector anda hyperbolic reflector, this view being substantially the same as FIG. 1of the '714 patent, but for the differences in the reference numerals.

FIG. 2 is a fragmentary sectional view thereof, taken generally on line2-2 of FIG. 1, this view being substantially the same as FIG. 2 of the'714 patent, but for the differences in the reference numerals.

FIG. 3 is a top plan view of the prior art optical rotary joint shown inFIGS. 1 and 2, this view showing the limited acceptance angle of theelliptical reflective surface for a receiver using an optical fiber.

FIG. 4 is a schematic representation of another form of prior artoptical rotary joint that includes an elliptical reflector arranged toreflect light emanating from a source at focal point F₁ to the entranceend of an optical fiber positioned at focal point F₂, this view beingsubstantially the same as FIG. 4 of the '714 patent, but for thedifferences in the reference numerals.

FIG. 5 is a schematic perspective view of the improved optical rotaryjoint, showing the transmitting optics as transmitting optical signalsto an elliptical reflector, at which they reflected to a conicalreflector, for re-reflection upwardly through a train of lenses towardthe entrance end of an optical fiber communicating with a photodetector.

FIG. 6 is a schematic perspective view of the improved optical rotaryjoint, similar to FIG. 5, in which the optical signals reflected back bythe elliptical reflective surface are focused on an arcuate slabcommunicating with the distal divergent ends of a fan-shaped fiberarray.

FIG. 7 is a schematic view showing the wider acceptance angle for thereceived signal in FIG. 5.

FIG. 8 is a schematic view of the architecture for transmitting data atthe rate of 80 Obit/sec through the improved optical rotary joint.

FIG. 9 is a schematic view of the electronic implementation to switchthe optical signal at different rotor positions, for carrying a largedata transmission rate across the rotary interface.

FIG. 10 is a schematic view showing the use of a buffer/multiplexer toachieve channel selection.

FIG. 11 is a schematic view showing the use of a crosspoint switch toachieve channel selection.

FIG. 12 is a perspective view of one form of an improved opticalreflector assembly.

FIG. 13 is a perspective view of the tooling plate for use in assemblingthe improved optical rotary joint, this view showing the annular innerportion and the arcuate outer portion provided with five pockets toreceive the reflector assemblies.

FIG. 14 is a perspective view, similar to FIG. 13, but showing theoptical reflector assemblies as having been placed in the tooling plateouter portion pockets.

FIG. 15 is a perspective view, similar to FIG. 14, but showing the gaugepins as having been placed in the V-grooves and the stator segment ashaving been placed over the reflector assemblies.

FIG. 16 is a perspective view, similar to FIG. 15, but showing the fourrotor segments as having been placed on the gauge pins of the toolingplate inner portion, and having been joined together to form anassembled rotor.

FIG. 17 is a perspective view, similar to FIG. 16, but showing the rotoras having been inverted and secured to the stator assembly usingbrackets.

FIG. 18 is a schematic view showing the use of a wavelength divisionmultiplexing technique to multiply the bandwidth of the data transmittedthrough the improved optical rotary joint.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

At the outset, it should be clearly understood that like referencenumerals are intended to identify the same structural elements, portionsor surfaces consistently throughout the several drawing figures, as suchelements, portions or surfaces may be further described or explained bythe entire written specification, of which this detailed description isan integral part. Unless otherwise indicated, the drawings are intendedto be read (e.g., cross-hatching, arrangement of parts, proportion,degree, etc.) together with the specification, and are to be considereda portion of the entire written description of this invention. As usedin the following description, the terms “horizontal”, “vertical”,“left”, “right”, “up” and “down”, as well as adjectival and adverbialderivatives thereof (e.g., “horizontally”, “rightwardly”, “upwardly”,etc.), simply refer to the orientation of the illustrated structure asthe particular drawing figure faces the reader. Similarly, the terms“inwardly” and “outwardly” generally refer to the orientation of asurface relative to its axis of elongation, or axis of rotation, asappropriate.

In one aspect, the present invention provides an improved optical rotaryjoint of the constant-path-length elliptical-reflector-based typedisclosed in the '714 patent, but having another and different element,namely, a second reflector having a second reflective surface configuredas a portion of a cone. The addition of this second reflector enablesthe improved optical rotary joint: (1) to transmit optical signals at ahigher efficiency, (2) to facilitate the transmission of such opticalsignals into the entrance end of an optical fiber, (3) to allow thenumber of light sources to be reduced, and (4) to reduce the opticalpath length from the light sources to the receiver.

While it is still acceptable to use a photodetector as the receiver inhigh data rate transmission through the rotary joint, it is sometimesdesirable, such as in an electrically-noisy environment, to first directthe transmitted signals into the entrance end of an optical fiber thatcommunicates with a remotely-located receiver. It is also desirable toenlarge the acceptance angle for such receiving optical fibers such thatsmaller number of light sources may be used. A reduction in the numberof light sources will lower the manufacturing cost of the improvedoptical rotary joint. Thus, the invention provides improved opticalrotary joints with associated optical assemblies, electronics, andmanufacturing methods to transmit optical data through the rotaryinterface into the entrance end of an optical fiber at an increasedacceptance angle, with a reduced path length, and at an increasedcoupling efficiency.

In another aspect, the invention provides an improved optical rotaryjoint in which light reflected from an ellipsoidal reflective surface isfocused onto an optical slab communicating with the distal divergentends of a fan-shaped fiber array having a plurality of optical fibershaving closely-adjacent divergent entrance ends positioned proximate thesecond focal point, and having exit ends arranged to guide light towardthe receiver.

In another aspect, the invention provides improved optical reflectorassemblies for use in such optical rotary joints.

In still another aspect, the invention provides improved methods ofassembling an optical rotary joint in an optically-aligned manner, andof mounting such assembled joint on a supporting structure whilepreserving and maintaining such optical alignment.

These various aspects will be discussed seriatim herebelow.

Improved Optical Rotary Joints (FIGS. 5-6)

FIG. 5 is a conceptual schematic of an improved optical rotary joint,according to the present invention, that is used to provide opticalcommunication across a rotary interface, such as between a rotor and astator, as previously described. In FIG. 5, the improved optical rotaryjoint, generally indicated at 35, as depicted as having an opticalsource 36 mounted on the rotor, a first reflector 38 mounted on thestator, a second reflector 39 also mounted on the stator, and a lightreceiver including a series of lenses 40 communicating with an opticalfiber 41 that leads to a remotely-located photodetector (not shown). InFIG. 5, the light source is depicted as being distal end of an opticalfiber 42. The light rays are shown as diverging outwardly from the fiberend, and then passing through a collimator lens 43. After passingthrough lens 43, the individual rays are slightly diverging as if comingfrom the focal point, F₁ and are directed at the first reflectivesurface 44 of first reflector 38. This first reflective surface ispreferably configured as a portion of an ellipsoid, in that it hascompound curvature in each of two orthogonal axes (i.e., x-y, and y-z).The first curvature, depicted by imaginary line L going from end to endin the horizontal direction (i.e., in the x-y plane), is configured as aportion of an ellipse having first and second focal points, F₁ and F₂,respectively. However, the first reflective surface is also curved inthe vertical direction (i.e., in the y-z plane). The compound curvatureof the first reflective surface cooperates such that light reflectedfrom an area on first reflective surface 44 converges toward apoint-like spot on second reflector 39.

In the disclosed embodiments, the second reflective surface 45 on secondreflector 39 is conical. However, the second reflective surface couldpossibly be frusto-conical, or some other portion of a cone. Asindicated above, the area of light incident on the second reflectivesurface is smaller than the area of light incident on the firstreflective surface, owing to the compound curvature of the ellipticalreflective surface. In the disclosed embodiment, the conical secondreflective surface 45 has an apex angle of about 45°. Hence, lightincident on second reflective surface 45 is directed upwardly into thetrain of lenses, indicated at 40. This train may include twoplano-convex lenses, two aspheric lenses, a lens and a holographicelement, or some other combination of lenses and/or other opticalelements. In any event, the function of this train of lenses is to focuslight into the entrance end of optical fiber 41, which conveys the lightto a distant photodetector (not shown).

The elliptical first reflective surface 44 has first and second focalpoints, F₁, F₂, that lie in the plane of line L. The first focal pointF₁ is positioned substantially coincident with the axis of the rotor.The second focal point F₂ is positioned along the axis of the cone 39.Thus, beams seen as originating at first focal point F₁ are incident onthe elliptical reflective surface 44, and are reflected to convergetowards the conjugate focal point F₂ inside the cone 39. The secondreflective surface further reflects the light upwardly in a directionnormal to the rays of light incident thereon.

The second reflector cone may be made of glass, plastic or metal, andmay be coated to reflect the maximum amount of light. An opticalsubassembly is placed above the reflective cone to focus the light intoa receiver. The receiver can be a photodetector or an optical fiber. Acone is effective because it collects light from a large area (i.e., thearea of the first reflective surface on which the collimated light beamsare incident), and directs it upwardly toward the receiver. Thisconvergence and change-in-direction overcomes the traditionallimited-acceptance angle of an optical fiber, and allows the receivingfiber to accept light signal from the extended area of the ellipticalreflective surface. In the disclosed embodiment, the second reflector isconfigured as a cone, and has an apex angle of 45° such that the lightrays will be reflected in a direction perpendicular to the direction ofthe rays incident thereon. While preferred, this arrangement is notinvariable. In appropriate cases, the second reflective surface mightpossibly be frusto-conical and/or might have an apex angle of other than45°.

The optical subassembly that focuses light from the cone toward thereceiver may include a train of lenses, or a combination of lenses and aholographic element. In FIG. 5, two plano-convex lenses are used tofocus the reflected beam from the cone into an optical fiber. Thisoptical subassembly can also consist of a lens and a volume hologramthat diffracts light into the receiving fiber. Alternatively, thesubassembly can be an array of ball lenses arranged around the axis ofthe cone. If the receiver needs to be mounted horizontally, aright-angle prism can be mounted between the two lenses to turn thefurther-reflected beams from the cone by 90°. If the light needs to bedirected at some other angle, then a mirror, a prism of some otherappropriate shape, or the like, may be used.

FIG. 6 is a variant form of the improved optical rotary joint. In thisform, the light reflected from the ellipsoidal first reflective surface44 is focused to converge on the arcuate slab that communicates with thedivergent ends of a fan-shaped array of optical fibers. Light enteringthese fibers is directed therealong, and is discharged at the convergentends thereof through a collimating lens 48 to a photodetector 49.

There are many advantages of these improved optical rotary joints. Suchdevices have substantially constant optical path lengths from the sourceto the receiver that are independent of the relative positions of therotor and stator. This constant path length enables multiple opticalsignals to be superimposed in the receiver without phase distortion.When a higher data transmission rate is desired and lasers that supportsuch a higher data rates do not have sufficient power, multiple opticalsources can be stacked to increase the optical power reaching thephotodetector.

Moreover, the improved optical rotary joint is independent of both thewavelength and the data transmission rate of the signals. The selectionof the wavelength for use with this device depends on the availabilityof the laser source, the photodetector, and the optical fiber thatcarries the optical signal. However, the improved optical rotary jointitself is data transmission rate-independent, and data transmissionrates ranging from DC through high gigabit/second can be used. Finally,wavelength division multiplexing can be used to transmit multipleoptical channels across the rotary joint when even higher data rates aredesired.

The improved optical rotary joints disclosed herein have additionalbenefits over the device described in the '714 patent. The improvedjoints: (a) reduce the variation of light intensity variation incidenton the face of the receiver, (b) reduce the effect of the acceptanceangle of the elliptical reflector, (c) allow the use of an optical fiberahead of the photodetector, and (d) reduce the optical path length.

These advantages are illustrated in FIGS. 7 and 8. In FIG. 7, an opticalreflector assembly, generally indicated at 46, is schematically shown asincluding an ellipsoidal first reflective surface 44 and a conicalsecond reflective surface 45, as previously described. Light signals aregenerated from sources 42. In FIG. 8, these various signal-transmittinglight sources are severally indicated at TX1, TX2, . . . , TX18, and thevarious optical reflector assemblies are severally indicated at CH1,CH2, . . . , CH16, there being one reflector assembly per channel.

In a simple elliptical reflector configuration, such as disclosed inFIG. 1 of the '714 patent, the position of the light source relative tothe elliptical reflector produces reflected beams with different anglesof incidence on the receiver. A beam incident on the ellipticalreflector near its edge converges at a greater angle of incidence withrespect to the normal to the surface of the receiver, than do those atnear the center. Since the sensitivity of the receiver drops off as afunction of the angle of incidence (i.e., the angle which the incidentbeam makes with a line normal to the surface on which the beam isincident), a beam with a larger angle of incidence causes the receiverto generate a smaller output signal.

In the present invention, the elliptical first reflecting surface ispreferably a portion of an ellipsoid. Hence, the compound nature of thisellipsoidal surface focuses the area of light incident thereon to a spoton the conical second reflective surface, as shown in FIG. 5. The lightconverging toward this spot is further reflected upwardly toward thereceiver. Hence, the further-reflected signal does not show a meaningfulchange in the angle of incidence at the receiver at different locationsof the source relative to the stator. As a result, the signal detectedby the receiver is substantially independent of the angle of incidenceof light incident on elliptical first reflective surface 44, and issubstantially independent of the position of the rotor relative to thestator. As a result, the number of sources used around the rotor can bereduced and minimized. The reduced drop off near the edges of theelliptical reflector is important because this helps to improve theminimum signal produced by the photodetector. The photodetector producesa minimum signal when a beam from one light source is just about toleave the reflector and a beam from an adjacent light source is justentering into the reflector. An increase in overlapping near the edgesof the reflector increases the amplitude of the superimposed lightsignals, and hence the signal produced by the detector, and thus reducesthe number of sources needed in the improved optical rotary joint.

An additional advantage of the present invention is in allowing the useof an optical fiber upstream of the receiver. In the '714 patent, use ofan optical fiber ahead of the receiver was seen to be hampered by thelimited NA of the fiber. As described herein, the improved compoundelliptical reflective surface focuses the reflected light to a spot onthe second reflective surface. The conical reflector surface is used toturn the reflected beams from the elliptical reflector toward thereceiver. Through the use of the cone reflector, the angle of incidencewith respect to the normal of the receiver surface is substantiallyconstant throughout the entire angle subtended by the ellipticalreflector. An additional optical subassembly above the cone may be usedto focus the convergent reflected beams into the entrance end of thereceiving fiber. The use of such an optical fiber can be particularlyuseful in areas where a high degree of electrical noise is present atthe rotary interface, or when it is desirable for remote detection ofthe signal. The use of a cone reflector enlarges the effectiveacceptance angle of the rotary joint. As shown in FIG. 7, the acceptanceangle for the rotary joint is increased to about 21.4°. With this largeracceptance angle, a minimum of seventeen light sources is needed forcontinuous trans-mission of signal across the rotary interface (i.e.,360°/21.4°=16.82≈17 sources).

The third advantage of using the cone reflector is in reducing theoptical path length. Using geometric analysis, the optical path lengthin the configuration shown in FIG. 7 is about 120 mm, which issignificantly less than optical path lengths (i.e, about 248 mm) in theconfigurations of FIGS. 1 and 4. The reduced optical path length reducesthe sensitivity of the improved optical rotary joint to misalignments.

By insuring that the optical path length is substantially constantthroughout the entire angle occupied by the elliptical reflector andthat sufficient optical power is directed into the receiving fiberthrough the reflection from the cone, the optical rotary joint of thepresent invention can support data transmission at data rates of 5.0Gbit/sec or more per channel. One data channel consists of oneelliptical reflector, a cone reflector, a subassembly of receivingoptics, a receiving fiber, and a high speed photodetector. Using anarray of data channels and the technique of switching data carried bythe sources around the rotor, very high data transmission rates can beachieved. An example is provided in FIG. 8, in which sixteen datachannels are arranged around the circumference of the rotary interface.Each of the data channels can carry optical data at a rate of 5.0Gbit/sec. By summing the sixteen data channels, an optical rotary jointcapable of passing 80 Gbit/sec (i.e., 16 channels×5.0Gbit/sec/channel=80 Gbit/sec) can readily be achieved using the presentarchitecture.

For example, as shown in FIG. 8, a fiber optic rotary joint includeseighteen sources, TX1 through TX18, respectively, spaced equally aroundthe circumference of the rotor at nominal interval angles of 20°. Thesources can emit the same optical signal, or different optical signals,as desired. In order to transmit the maximum amount of data across therotary interface, most of the sources carry different signal streams.The stator in the improved optical rotary joint is divided into sixteensectors. A sector contains one data channel, and the sector boundariesare marked by the radial hash marks shown in FIG. 8. Before a sourceenters a waveguide, it is selectively switched to provide the opticalsignal for that particular data channel. For example, source TX1 carriesthe optical data for channel CH1, source TX2 carries a different set ofdata for channel CH2, and so on. Where two sources are within onesector, both sources are switched to carry the same data signal. Forexample, in FIG. 8, sources TX5 and TX6 both carry the same signal forchannel CH5. Because of the constant path length property of the rotaryinterface, the optical signals from sources TX5 and TX6 can besuperimposed constructively, and the detector receives a strongerin-phase signal from the two sources. Thus, the superposition of the twosignals improves the quality of the superimposed amplitude-summedoptical signals by increasing the optical intensity of the two separatein-phase signals arriving at the photodetector.

Electronic Switching (FIGS. 9-11)

FIG. 9 illustrates the manner by which the improved optical rotaryjoints may be utilized to transmit data at a high transmission rate.Upstream of the optical rotary joint, an 80 Gbit/sec signal is dividedor deconstructed into sixteen 5.0 Gbit/sec signal streams utilizingconventional digital electronics. The sixteen 5.0 Gbit/sec signalstreams are routed via the channel selector to different respectivegroups of optical sources, TX1 through TX18, respectively, fortransmission across the rotary joint to sixteen receivers, RX1 throughRX16, respectively. If more than eighteen optical sources are used, thenmore than sixteen transmission channels can be established. After thesignals have been received, they are reconstructed to re-form theoriginal 80 Gbit/sec signal.

The optical rotary joint of this embodiment may include an angularposition encoder to track the location of the rotor relative to thestator such that the channel selector can appropriately switch thevarious 5.0 Gbit/sec signal streams to their respective sources. Thus,the fiber optic rotary joint of the present invention can readilytransmit optical signals at extremely high data rates.

It is important to note that a 5.0 Gbit/sec signal is not the bandwidthlimit of the rotary joint. In fact, any data rate up to 5 Gbit/sec couldbe utilized and when the electronics are readily available, data ratesof 10 Gbit/sec and higher can be implemented.

In another embodiment, the transmitter could accept a plurality of lowerdata rate signals, which are then multiplexed together to achieve ahigher data rate around 5 Gbit/sec. This data stream could be sentacross the rotary joint and reconstructed into the lower data ratesignals.

Two approaches are available for causing the channel selector to switchthe sixteen channels of source signals to the eighteen optical sourcesaround the rotor. The first approach involves a buffer/multiplexermethod as described in the U.S. Pat. No. 6,385,367, the aggregatedisclosure of which is hereby incorporated by reference. A schematic ofthis method is shown in FIG. 10.

According to this approach, each of the sixteen signals is fed into aseparate 1-to-18 buffer, which fans out the input signal into one of theeighteen multiplexer (MUX) channels. Eighteen MUX channels havingsixteen inputs are employed to receive the inputs from each of thebuffer chips. The rotor position encoder provides the locations at whichthe lasers are switched to carry data from another input signal stream.

While this approach generally works, when the number of input channelsincreases, the number of interconnections between the fanout/bufferchips to the MUX chips increases significantly. For example, if thereare M input signal streams and the number of sources around the rotorring is N, the number of interconnections (N_(interconnects)) is:N _(interconnects)=2M×N

The increase in the number of interconnections increases the complexityof the printed circuit board, and further spatially separates the chipswhich may introduce waveform distortion because of the length of thetransmission lines. The large number of buffers and other ICs increasesthe amount of propagation delay variation that is observed between thevarious paths. When these signals are added together at the opticaldetector, the variation in propagation delay causes the waveform to bedistorted and the observed eye pattern to close.

Another approach for channel selection can be achieved by using anon-blocking crosspoint (crossbar) switch, as shown in FIG. 11. An M×Ncrosspoint switch has the advantage that all the interconnections isbased on crosspoint switches, and the interconnections are allintegrated into the chip. Thus, no external interconnections are needed.An M×N crosspoint switch has the ability to spatially connect any one ofthe M inputs to any of the N outputs, and its functional schematic isshown in FIG. 11. A non-blocking switch insures that all inputs can beconnected to the respective outputs, and no transmission will be blockedby the other connections. The multicast capability enables one input toconnect to multiple outputs at the same time, while insuring each outputis connected to only one input.

A number of advantages result from use of a crosspoint switch. Theseinclude reducing the board size and chip count, reducing powerconsumption, and minimizing signal distortion. For example, in a typicalfour-input channel transmitter board, by employing a crosspoint switchover the buffer/MUX approach, the size of the board may be reduced byabout 30%, the number of chips may be reduced by over 20%, and the powerconsumption may be reduced by more than 40%. Because of the integrationof the switches into one die, the crosspoint switch generally minimizesthe signal distortion and reduced jitter, as compared to the buffer/MUXapproach. In fact, the variation in propagation delay in the crosspointswitch-based transmitter can be reduced by over 80% over the buffer/MUXapproach. This allows higher data transmission rates through the rotaryinterface. Another benefit of the crosspoint switch is the addedflexibility of transmitted data patterns. Because the crosspoint switchis transparent to data rates and protocol, multiple transmissionchannels can be established with each carrying a unique protocol atvarious data rates.

Improved Optical Reflector Assemblies (FIG. 12)

Referring now to FIG. 12, an improved optical reflector assembly isgenerally indicated at 50. The improved reflector assembly is shown ashaving three plate-like members sandwiched together, as described infra.The first or middle member 51 is shown as having an ellipsoidalreflective surface 52, as previously described. This intermediate memberhas a planar upper surface and a planar lower surface.

The reflector assembly also includes a lower second member 53. This isalso a plate-like member, and has a planar upper surface engaging theplanar lower surface of the intermediate first member 51. The secondmember 53 is shown as supporting a fourth member 54 having a conicalreflective surface 55. The second focal point of the ellipsoidal surfaceis substantially located on the axis of the cone object 54. Thereflector assembly is further shown as including a plate-like thirdmember 56. This third member has a planar lower surface that engages theplanar upper surface of intermediate member 51. The third member isshown as supporting the receiving optics, generally indicated at 58,which communicates via an optical fiber 59 with a remotely-located photodetector (not shown). The receiving optics may be a series or train oflens, to focus light into the entrance end of fiber 59.

The improved optical reflector assembly is thus simple to manufactureand construct. Of course, care must be taken in forming the ellipsoidalreflective surface 52 on the first member. The lower second member isshown as providing a support for the conical reflector, and the upperthird member is shown as providing a suitable support for the receivingoptics, which are aligned with the conical reflector. The device shownin FIG. 12 operates substantially as previously described. Theellipsoidal surface as a first focal point which is substantiallycoincident with the rotary axis. Thus, light which is seen as comingfrom the rotor axis, can be reflected from surface 52 to a spot onconical reflective surface 55, and then be re-reflected upwardly throughthe receiving optics into optical fiber 59. The device shown in FIG. 12will operate substantially as schematically shown in FIG. 5.

Improved Mounting Methods (FIGS. 13-17)

Referring now to FIGS. 13-17, this invention also provides, in anotheraspect, improved methods of assembling an optical rotary joint, andmounting such an assembled rotary joint on a supporting frame.

This method begins with the provision of a tooling plate, generallyindicated at 60, having an annular inner portion 61 provided with aplurality of circularly-spaced radially-extending V-grooves, severalindicated at 62, and having an arcuate outer portion 63 provided with aplurality of circularly-spaced pockets, severally indicated at 64. Eachpocket is adapted to receive a reflector assembly, such as previouslyindicated at 50 in FIG. 12, and to hold position such reflector assemblyin a predetermined position relative to the proximate V-grooves. Thus,FIG. 13 simply depicts the upper surface of the tooling plate. Greatcare is taken in machining the tooling plate, and this assembly ispreferably of a unitary one-piece construction.

The next step then is to provide a plurality of optical reflectorassemblies, such as indicated at 50 in FIG. 12.

Referring now to FIG. 14, the next step then is to physically place anoptical reflector assembly 50 in each pocket. The pockets are preferablymachined such that the optical reflector assembly will be received inonly one way, and that the reflector assembly will be properly orientedwith respect to the V-grooves on the tooling plate inner part.Continuing to refer principally to FIG. 15, a stator segment 69 is thenprovided, and this is placed on top of the optical reflector assemblies.The optical reflector assemblies is then mounted to the stator segmentto form an assembled stator. The assembled stator is now removed fromthe tooling plate.

The next step then is to place cylindrical gauge pins in at least someof the tooling plate V-grooves, as shown in FIG. 15. The various gaugepins are indicated at 65.

Thereafter, a plurality of rotor segments, severally indicated at 66 areprovided. These are positioned on top of the tooling plate inner part.Each rotor segment has a radially-extending V-groove that is adapted tobe aligned with the V-grooves in the tooling plate. Thus, as the variousrotor segments are placed on the cylindrical gauge pins, they will beproperly orientated with respect to one another.

Thereafter, the rotor segments are joined to form an assembled rotor,generally indicated at 68 in FIG. 16.

The assembled rotor is then removed from the tooling plate, and thegauge pins are removed from the tooling plate V-grooves. The assembledrotor is then inverted, and attached to the assembled stator through theuse of a plurality of precision machined brackets. A plurality of fiberand collimator assemblies are then provided, and these are mounted inthe assembled rotor V-grooves.

The assembled rotor and stator segment are thereafter mounted on asupporting frame, such as on the gantry of a CT-scan machine.Thereafter, the brackets are subsequently removed such that theassembled rotor and stator will be mounted on the supporting frame inthe desired alignment with respect to one another.

If desired, the method may comprise the additional steps of placing atest fiber and collimator assembly in one of the tooling plate V-groovesin FIG. 14; and testing the integrity of the optical connection betweenthis optical fiber and collimator assembly and the proximate reflectorassembly before removing the assembled rotor from the tooling plate.

Wavelength Division Multiplexing (FIG. 18)

The fiber optic rotary joint of the present invention also supports thetransmission of optical signals having different wavelengths, asdepicted in FIG. 18. In this embodiment, the fiber optic rotary jointincludes two or more lasers or other light sources for providing opticalsignals having different respective wavelengths. The optical rotaryjoint of this embodiment may also include separate same-length opticalfibers for transmitting the different-wavelength optical signals fromthe respective lasers or other light sources to the rotary interface.Alternatively, the optical source may include a fiber coupler, as alsoshown in FIG. 18, for combining the optical signals having differentwavelengths such that the combined optical signals can be transmitted tothe rotary interface by means of a common optical fiber.

In this embodiment in which optical signals having different wavelengthshave been combined, the receiver may be configured to include asplitter, such as a dichroic filter, for separating thedifferent-wavelength optical signals, and to include a plurality ofphotodiodes or other detectors for receiving the separated opticalsignals. In the embodiment in which the receiver is remote from therotary interface, the different-wavelength optical signals propagatealong a common optical fiber prior to being collimated, such as by acollimating lens, and then split in accordance with the wavelength ofthe optical signals.

By utilizing wavelength multiplexing, the bandwidth may be increasedwithout increasing the modulation rate of the optical sources. Since thecosts associated with increasing the modulation rate of the opticalsources may be substantial at larger data rates, the inclusion of two ormore sets of lasers or other sources that provide optical signals withdifferent wavelengths may sometimes be more economical. Using thistechnique, an optical rotary joint capable of transmitting data at arate on the order of 160 Gbit/sec can be achieved by using twowavelengths.

Modifications

The present invention contemplates that various changes andmodifications may be made. For example, the first reflective surfaceshould be configured as a portion of an ellipse having first and secondfocal points. This surface is preferably configured as a portion of anellipsoid in that it has a compound curvature in two perpendicularorthogonal axes, such that the area on the ellipsoidal surface on whichlight is incident will be reflected toward, and will converge at a spoton the conical reflector.

As used herein, the second reflector is shown as being a cone, and has a45° apex angle. However, this is not invariable. In some situations, thesecond reflector may be frusto-conical, or may have some otherconfiguration of a portion of a cone. In any event, the salient here isthat the function of the conical reflector is to re-reflect light in adifferent direction toward receiving optics, which may include a trainof lenses or the like. Alternatively, the re-reflected light may beincident directly on the operative surface of a photo detector.

The various materials of construction may be changed, as will be readilyappreciated by persons skilled in this art. The various reflectivesurfaces may be coated and/or polished to provide a high degree ofreflectivity.

Therefore, while several aspects and embodiments of the presentinvention have been shown and described, and various modificationsthereof suggested and discussed, persons skilled in this art willreadily appreciate that various additional changes and modifications maybe made without departing from the spirit of the invention, as definedand differentiated by the following claims.

What is claimed is:
 1. An optical reflector assembly (50) for enablingoptical communication between a rotor and a stator, said rotor having alongitudinal axis, comprising: a first member (51) having a concavefirst reflective surface (52), a line (L) in a plane taken through saidfirst reflective surface being configured as a portion of an ellipsehaving first and second focal points (F₁, F₂), said first focal point(F₁) being positioned substantially coincident with said rotor axis; asecond member (53) mounted on one side of said first member (51); athird member (56) mounted on the opposite side of said first member(51); a fourth member (54) mounted on said second member (53) and havinga second reflective surface (55) having a longitudinal axis; receivingoptics (58) mounted on said third member (56) such that an opticalsignal seen as originating from said first focal point (F₁), fallingincident on said first reflective surface (52), and being furtherreflected toward said second reflective surface (55) will be furtherreflected toward said receiving optics; and an optical fiber (59) havingan entrance end and an exit end, said entrance end being arrangedadjacent to said receiving optics; and wherein said first reflectivesurface (52) is configured as a portion of an ellipsoid and said secondreflective surface (55) is configured as a portion of a cone positionedat the second focal point (F₂) of said first reflective surface (52)such that an optical signal reflected by said first reflective surface(52) toward said second focal point (F₂) converges to a spot on saidsecond reflective surface (55) and is reflected in a different directionas a function of the apex angle of said cone of said second reflectivesurface (55), the area of said spot on said second reflective surfacebeing smaller than the area on said first reflective surface (52) wheresaid optical signal is incident for reflection toward said second focalpoint (F₂).
 2. An optical reflector assembly as set forth in claim 1wherein said second reflective surface (55) has a longitudinal axis andwherein said receiving optics (58) is substantially aligned with saidsecond reflective surface longitudinal axis.
 3. An optical reflectorassembly as set forth in claim 1 wherein said first member (51) is aplate having opposite planar surfaces.
 4. An optical reflector assemblyas set forth in claim 3 wherein said second member (53) has a planarsurface arranged to engage one of said first member planar surfaces. 5.An optical reflector assembly as set forth in claim 4 wherein said thirdmember (56) has a planar surface arranged to engage the other of saidfirst member planar surfaces.
 6. An optical reflector assembly as setforth in claim 1 wherein said second member (53) is a plate.
 7. Anoptical reflector assembly as set forth in claim 1 wherein said thirdmember (56) is a plate.
 8. An optical reflector assembly as set forth inclaim 1 wherein said conical second reflective surface (55) has an apexangle of about 45°.
 9. An optical reflector assembly as set forth inclaim 1 wherein said receiving optics (58) includes an aspheric lens anda ball lens.
 10. An optical reflector assembly as set forth in claim 1wherein said receiving optics (58) includes a pair of aspheric lenses.11. An optical reflector assembly as set forth in claim 1 wherein aphotodetector is arranged adjacent to said optical fiber exit end.